to meet your requirements all you need is 4 diodes & a really big Capacitor. 5 parts, maybe 2$ to build.
form the diodes into a "full wave rectifier" form and put the capacitor on the output. the capacitor is what will give you the DC output.
of course, you will not get a pure DC output, there will be some voltage ripple, but even the most expensive AC/DC converters always have some ripple. since your requirements do not specify the minimum ripple, then it is not a concern to you!
Mr.Cool